1. Field of the Invention
The present invention relates to a main shaft locating mechanism for change of tool, and more particularly to a locating mechanism wherein an eccentric locating pin is axially fitted with an eccentrical hole of a locating seat and the main shaft stops rotating before the tool changing mechanism loosens the tool.
2. Description of the Prior Art
It is known that the tool mounted on a main shaft of a machining device must be frequently changed according to the shape and material of the work piece or due to abrasion or damange of the tool. For facilitating the change of the tool, the machining device is often provided with an automatic tool changing mechanism. At the time of changing the tool, the position of the handle of the tool is often needed to be identified. Therefore, it is necessary to locate the main shaft before changing the tool. The conventional main shaft locating mechanisms can be divided into electronic type and mechanical type. The former usually includes several sensing elements for detecting the position of the main shaft and a driver for locating the main shaft at a desired position. The cost for such electronic locating mechansim is often considerably high. On the other hand, the mechanical locating mechanism usually includes a hydraulic cylinder, a piston, a piston stem and cooperative closely spaced switches. Such locating mechanism is mostly disposed on a lateral side of the main shaft to radially displace for locating the main shaft. This increases the dimension of the main shaft and causes inconvenience with respect to a main shaft contained in a housing with limited dimension (such as an internally hidden main shaft of a motor). Moreover, the locating operation is achieved by direct contact so that the abrasion of the main shaft will be relatively great. Although the locating operation can be achieved alternatively by rollers, a problem of undesired clearance will take place.